Hydraulic drive for planers and the like



Jan; T8, 1 955 J.'K. DOUGLAS 2,699,651

HYDRAULIC DRIVE FOR PLANERS AND THE LIKE Filed Aug. 24, 1953 5 Sheets-Shet 1 IVNVEN'IV'O'R JAMESKDOUGLAS ATTORNEY Jan. 18, 1955 J. K. DOUGLAS 2,699,651

HYDRAULIC DRIVE FOR PLANERS AND THE LIKE Filed Aug. 24, 1953 5 Sheets-Sheet 2 8 I "1 I2 I mvsmon JAMES KDOUGLAS ATTORNEY Jan. 18, 1955 J. K. DOUGLAS 5 HYDRAULIC DRIVE FOR FLANERS AND THE LIKE Filed Aug. 24, 1953 5 Sheets-Sheet 3 INVEINTOR J MESKDOUGLA ATTORNEY Jan. 18, 1955 .1. K. DOUGLAS HYDRAULIC DRIVE FOR PLANBRS AND THE LIKE Filed Aug. 24, 1953 5 Sheets-Sheet 4 INVENTOR J AMES KDOUGLAS I w ATTO NEY Jan. 18, 1955 J. K DOUGLAS ,651

HYDRAULIC DRIVE FOR PLANERS AND THE LIKE Filed Aug.- 24, 1953 5 Sheets-Sheet 5 LI) L21 FIG. 7 L3 L5 SS2 ssl 1 [*9 0* mold u INVENTOR JAMES K DOUGLAS ATTORNEY United States Patent HYDRAULIC DRIVE FOR PLANERS AND THE LIKE James K. Douglas, Shorewood, Wis., assignor to The Oilgear Coinpany, Milwaukee, Wis., a corporation of Wisconsm Application August 24, 1953, Serial No. 376,038

22 Claims. (Cl. 60-52) This invention relates to hydraulic drivers of the type employed to drive a machine part or other element through predetermined linear or angular distances in opposite directions alternately, such as the drive shown in Patent No. 2,465,212.

A drive constructed according to the invention is parti'cul'arly adapted to drive the table of a bed planer and the invention will be explained as being employed for that purpose but it is to be understood that the invention is not limited to a planer drive and that drives embodying the invention may be employed to drive machine parts or other elements which are to be reciprocated or rotated in opposite directions alternately.

A hydraulic planer drive includes a hydraulic motor for driving the table of the planer, a pump for supplying liquid to the motor to energize it, means to control the rate and direction of flow of liquid to thereby control the speed and direction of table movement and means for reversing the flow of liquid to thereby reverse the direction of table movement. In order to keep control of the planer table, the pump and motor ordinarily'are connected into a closed circuit. That is, the pump and motor are connected in series so that all of the liquid discharged by the pump flows to the motor and all of the liquid discharged from the motor is returned to the pump.

When the planer is taking a heavy cut or is operating upon tough material, the table will vibrate longitudinally due to variations in tool resistance and t0 the elasticity of the motive liquid. A

The present invention has as an object to provide a drive which will drive an element in opposite directions.

alternately and will reverse the element at substantially the same point each time regardless of its speed and in which table vibrations are reduced to a minimum.

Another object is to provide a drive which has all the advantages of the drive shown in Patent No. 2,465,212

and which is controlled electrically.

Another object is to provide a hydraulic drive which is very accurate in operation and is susceptible of close adjustment and control.

Other objects and advantages will appear from thefollowing description of the hydraulic drive shown schematically in the accompanying drawings in which the views are as follows:

Fig. 1 is a diagram of the hydraulic circuit of a planar drive in which the invention is embodied.

Figs. 2 and 3 are views showing a speed range selector valve in positions diiferent from that shown in Fig. 1.

Fig. 4 is an enlarged view illustrating the displacement varying mechanism of the pump shown in Fig. 1.

Fig. 5 is a diagram of the hydraulic circuit which controls the displacement varying mechanism of the pump shown in Figs. 1 and 4.

Fig. 6 is a view similar to the lower righthand portion of Fig. 5 but showing certain valves in positions different from those shown in Fig. 5.

Fig. 7 is a diagram of an electric circuit for controlling tshe s1ol6enoids which operate the valves shown in Figs.

Fig. 8 is a schematic representation of the magnetic switches employed in the circuit shown in Fig. 7.

Fig. 9 is an enlarged plan view of a follow-up device shown in Fig. 5.

Fig. 10 is a view taken in the plane indicated by the line 1010 of Fig. 5 but drawn to a larger scale.

Patented Jan. 18, 1955 For the purpose or illustration, the drive has been shown as being employed to reciprocate table 1 or a conveniional planer. omce such a planer 18 well Known and torms no part of the present invention, only the table thereor has been illustrated. Table l is reciprocated by a hydraulic motor which may be or the rotary type, as shown in raient No. 2,403,212, or or the reciprocating type. A reciprocating hydraulic motor may comprise a single double acting cylinder or two opposed single acting cylinders, in which case the drive would have only a single range or speeds, or the drive may comprise a combination or double acting and single acting cyimders in wnich case the drive would have a plurality or speed ranges.

in order to simpiiiy the drawings, the hydraulic motor has been shown in Fig. l as having two stationary cylinders 2 and 3 arranged in axial aimement, a piston 4 fitted in cylinder 2 and connected by a rod 5 to we left end of table 1, and a ram 0 extending into cylinder 3 and connected to the right end of table 1. But in practice the cylinders are arranged alongside each other in order that the table may have a maximum Stroke and three cylinders may be employed instead of two in order to avoid exerting transverse rorces upon the table.

Liquid tor energizing the hydraulic: motor is supplied thereto by a reversible variable displacement pump P1 which is driven by an electric motor lvll. Pump P1 when driven will deliver liquid to the motor and have liquid returned to it through one or the other of two channels 7 and 8 and thereby cause the motor to drive table 1 at a speed proportional to the displacement of pump P1.

liston rod 5 and ram 6 have the same cross-sectional area so that, when pump P1 supplies motive liquid to the motor at a given rate, liquid will bereturned to pump Pi from the motor at substantially the same rate. The

1 cross-sectional area of rod 5 bears such a ratio to the rate would cause the motorto move table 1 toward the cally controlled and which is formed in a valve body 11 as indicated by the full right at a low speed, liquid delivered at the same rate to the left end of cylinder 2 only will cause the motor to move table 1 toward the right at an intermediate speed which is twice the low speed, and liquid delivered at the same rate to cylinder 3 only will cause the motor to move table 1 toward the right at a high speed which is three times the low speed.

In practice, the drive is provided with a system of valves which are hydraulically operated and electrienable the motor to advance the table on a cutting stroke at a selected speed in any one of the speed ranges and to retract the table at a selected speed in the high speed range. But in order to simplify the drawings, the drive has been shown provided with a selector valve 9 able the motor to advance table 1 at a selected speed within any one of three speed ranges and to retract table 1 at a selected speed within the same speed range.

As shown, selector valve 9 is fitted in a bore 10 which or ports 12, 13, 14, 15 and 16 formed in its wall. Channel 7 is connected to port 14. Channel 8 is connected to the right end of cylinder 2 and to port 12 which is also connected by a channel 17 to port 16. Port 13 is connected to the left end of cylinder 2 by a channel 18 and port 15 is connected When valve 9 is in the pump P1 is discharging liquid into channel 7, liquid will flow from channel 7 through bore 10 and channel 19, arrows, to cylinder 3 and act thereby causing ram' 6 to move table 1 toward the right at a selected speed within the high speed range. Movement of table 1 toward the right will cause piston 4 to expel liquid from the right end of cylinder 2 into channel 8. The expelled liquid upon the end of ram 6,

1 f and in part through bore 10 and channel 18 to the end of cylinder 2 as indicated by the dotted arrows.

which is adjustable to enand has five annular grooves to cylinder 3 by a channel 19.. position shown in Fig. 1 and.

will flow in part through channel 8 to the intake of pump age-09,851

the same paths but in the opposite direction. The liquid delivered to the right end of cylinder 2 will cause piston 4 to move table 1 toward the left at a selected speed within the high speed range.

When valve 9 is in the position shown in Fig. 2 and pump P1 is dischargingliqu-idinto'channel 7, liquidwill flow from channel '7 through bore 14) and 'channel I8, as indicated by =the fullarr'ows, *tothe left 'end of'cylinder 2 and act upon the left end of piston 4, thereby causing piston -4 to move table -1 toward 'the right at a selected speed within the intermediate speed range and -to expel liquid from the -right-end of cylinder -2 into channel 8. lhecxpelled liquid will llow in part through channel 8 to the intake of pump P1 and in-part through port 12, channel .17,=bore IO-andehannel 19, -as-indicatedby-the dotted arrows, to cylinder 3 to i-reep -it:fillerl as ram 6 moves toward the 'right. Reversabofpurnp -P-1 will'cause liquid to fiow through the same paths but in 'oppo-Site'directions. Theliquid-delivered to the right endofcylinder 2 will cause piston 4 to move table -1 toward the left .at a selected speed within the intermediate speed range.

When .val-ve 9 .is in the position shown in Fig. 3 and pump P1 is :discharging liquid into channel 7, liquid will fiow-sfrom channel .7 through bore 10 and channels 18 and 19, :as indicated by the full arrows, to cylinder 3 and to the left end of cylinder 2. 'Iihe liquid entering cylinder twilliact upon-the left -endof piston 4 and the liqnidentering cylinder.3 will act .upon the end-of ranr6, thereby causing piston 4 and ram 16 to .move table 1 toward the right at :a selected :speed within the low speed range. .Movement .of itable 1 toward the right will cause piston -4 to dispel liquid :from the rightend of=oylinder 2 through channel 8, asindicated .by.the dotted arrows, to the intake .of pump .Pl. Reversal of pump -P-1 willcause liquid .to -flow .through the same path but in the opposite direction. The .liquid :deliveredtto :the right end of cylinder .2 will :cause ppiston 4'to move table 1 :toward the left at .a selected .speed within the lowspeed .range.

Table 1111111811 bezaccelerated at the .beginningof each stroke in :each direction and must .be .decelerated near the end of each stroke .in each direction. Table 11 is accelerated :and decelerated by means to be presently described. The .rate .at which .the .table should the accelerated .or 'decelerated'when the .drive .is operating vin the high speed range :is different ifrom the :rate 'at which athe tablelshould be accelerated or :decelerated'when the drive is operatingiin the intermediate :range :or the low :speed range. .As wlillpresentlyhe explained, selection between those rates :is accomplished .by .means including .a limit switch LS 1 which .is open when the drive is operating in the high speed range and is closed when the sdriveris operating in .a lower speed range. .As shown, :switch LS1 liquid to flow 'from channel '28 into either channel 7 or range selector valving forms no part of the present invention, the third pump has not been illustrated and the drive has been shownas having the backipressure on the motor supplied by pump P2, as will presently be explained, but it is to be understood that the use of a third pump 'is preferable inorder that pump P2 may 'besrriall and the back control pressure.

THE MAIN PUMP Since pump P1 is a standard commercial type, it is deemed stifiicient to state herein that -it "has a pumping mechanism arranged within a displacement varying member or s'lideblock 35 (Fig. 4*) 'which is arranged within the casing 36 -of the pump, that pump displacement will be zero when Slideblock 35 is in its central or "neutral position and that "the pump will deliver liquid in a direction and at a rate-dependent upon the direction and distance that slideblock 35 is shifted from its neutral position. More specifically, pump P1 will discharge -liquid into channel 7 'and have liquid returned to 'it through channel 8 when slideblock 35 is moved from its neutral position downward in respect to Fig. 4 and 'it will dis'cha'rge liquidinto channel 8 and have liquid returned to its through channel 7 when slideblock 35 is lrgr'ovtilfrom its neutral position upward in respect to Movement of s'lideblock 35 upward in respect to Fig.

4 is effected -by =a servo-motorcomprising a cylinder 37, which is arrange'din thewall of casing'36 at one side of slidblock 3'5, "and apist'on 38 which is fitted in cylinder 3?] .and eng'ages 'slideblock 35. Cylinder 37 is closed at its outer end by -an end head 39. "Movement of slideblock 35 downward in respect to Fig. 4 i's'effected -by a servo-:m'o'tor comprising a cylinder 40, which is arranged is operated bya cam .20 .fixed IUPGH the .stem of valve :9

in such .a position that it will .close switch LL51 when valve 9 is shiftedfrom theposition :sho'wn in.:Eig. 1 into i h e pgsition showninsFig. .2 orrinto the position-shownain g. Except for its controls, pump P1 isz'a standard :commercial type of :pump which :is mounted upon a base (not shown) and which has :an auxiliary pump .driven in unison therewith and "arranged in the casing thereof. However, the auxiliary pump P2 has 'been shown "in "Fig. 1 outside nf the casing ofwoump P1 in order to illustrate the auxiliary pump circuit.

Pump R2 draws liquid from :a reservoir-.25, which is in 'the base of pump P1, anddischarges it -into=a branched control channel 26 :having one'of .its branches connected to the inlet of .a :relief 'valve 27 the outlet of which is connected to .a branched channel '28 having one branch thereofzconnec'ted to a low pressure relief valve "29 which discharges into reservoir 25. Asecond branch'of channel '28 is connected to channel 7 and-hasa check valve 30 connected therein. A third "branch -o'f-c'hannel 28 is connected to :chann'el 8 and has a check valve '31 connected therein. .Relie'f valves -27 and 29, channel 28 and checkvalves 30 "and 31 are arranged within the 'base and easing of pump Psl and do not appear in Fig. *4.

,pump P2 is running, it discharges liquid continuouslyvzflrrough "relief valves 27 and -29 into reservoir 25. Relief valve 1277 enables pump P2to ma'intain asuitable control pressure in channel 26 and relief'valve 29 enableszpump P2 to "maintain a low"-pressure in'channel 28. 'Check valves 30 and 31 prevent liquid fromil'owing from channels 7 and 8 into channel 28 but permit inthewall of casing 36 at the other side of slideblock 35, Sand a piston -'41 which is fitted in cylinder 40 and engages slid'eblock35. Cylinder 40 is 'closed'at its outer end byia valveb dy 42 having acap 43 on its outer end.

servoa'motors .3738 and -4041 are both operated by liquid supplied thereto from pump PI2 =at ethe same pressure but piston 38 is considerably larger than .piston 41 so that, when both of cylinders .37 and 40 areconnectedsto pump P 2, liquid willifiow into cylinder 37 and cause piston '38 to move slidebloclp3 5 upward in respect to Fig. 4 against the resistance of piston 41 and, when cylinder 40 is connected to pump P2 and cylinder 37 is connected to exhaust, liquid will flow into cylinder 40 and cause piston 41 to move 'slideback '35 in the opposite direction. Liquid for operating servo-motor 40-41 is continuously available thereto from pump P2 but the flow of liquid into and 'out of cylinder 37 is controlled by a pilot valve and the rate at which liquid can flow into or out of cylinder 37 is regulated to thereby cause slidehlock .35 :to be moved at a regulated rate as will presently biz-"explained.

LOCKING 'OFIMAIN CIRCUIT Valve body 42 has formed therein a valve bore 47 whichcommunicates at one'end'witha cylinder 40 and at its other end with a spring chamber 48 the outer end of which is closed by cap 43. 'B'ore 47 has formed in the wall thereof four annular grooves or ports 49, 50, 51 and '52. Port 50 is connected to cylinder -40 by a channel 53. Port 49 and spring chamber 48 have a branch of control channel 26 connected thereto. Port 52 has connected theretoa back pressure channel 126" which has been shown as :being .a branch of channel 26 but in practice the back pressure channel is connected to the third pump previously mentioned and it cornmunica'tes with the relief valve of that pump.

Communication between the several ports 4952 is controlled by a locking valve 54 which is fitted in bore pressure be considerably higher than the 47 and is spring centered in the position shown in Fig. 4 by a caged spring 55 arranged in spring chamber 48. Valve 54 moves with piston 41 as will presently be explained. In order to permit valve 54 to be spring centered, the piston thereof which normally covers port 49 is provided in its peripheral surface with a small axial bleed groove 56.

The function of locking valve 54 is to unlock the main hydraulic circuit by establishing communication between the return side of the main hydraulic circuit and the back pressurechannel when the hydraulic motor is driving table 1 at a cutting speed in the cutting direction and to lock the main hydraulic circuit, that is to block communication between the main hydraulic circuit and the back pressure channel when table 1 is being accelerated or decelerated.

Valve body 42 also has formed therein a valve bore 60 having three annular grooves or ports 61, 62 and 63 formed in the wall thereof. Port 61 is connected by a channel 64 to port 51. Ports 62 and 63 are connected, respectively, by channels 65 and 66 to channels 7 and 8 respectively. Communication between ports 61, 62 and 63 is controlled by a selector valve 67 which is fitted in bore 60 which is held in engagement with piston 41 by a spring 68 which is arranged in the outer end of bore 60 and reacts against cap 43.

The function of valve 67 is to determine the side of the main hydraulic circuit into which back pressure can extend when slideblock 35 is oifset from its neutral position and to permit bypass of liquid between channels 7 and 8 when slideblock 35 is in its neutral position. If the planar is to cut in either or both directions, valve 67 is made substantially as shown so it will not block either of ports 62 and 63 but if the planer is to cut in one direction only, valve 67 may have the innermost piston thereof made of such a length that it will extend into port 62 when valve 67 is in its neutral position and will block port 62 when valve 67 is moved a very short distance upward in respect to Fig. 4.

The arrangement is such that, when slideblock 35 and valves 54 and 67 are in their neutral positions as shown in Fig. 4, port 51 is open to port 52 and there is a slight opening between port 61 and each of ports 62 and 63 so that the pressure in port 52 can extend through port 51 and channel 64 into port 61 and extend therefrom through port 62 and channel 65 into channel 7 and through port 63 and channel 66 into channel 8. If slideblock 35 should wander slightly from its neutral position, any liquid discharged by pump P1 into channel 7 or 8would be bypassed through channels 65 and 66, ports 62 and 63 and bore 60 but slideblock 35 would immediatcly be brought back to its neutral position by a control to be presently described.

When liquid is supplied to cylinder 37, piston 38 will move slideblock 35 and piston 41 upward in respect to Fig. 4 and cause pump P1 to discharge liquid into channel 8 immediately after slideblock 35 moved beyond its neutral position. Valve 67 will move with piston 41 and only a slight movement thereof beyond its neutral position is required to cause it to block communication between ports 62 and 63, thereby closing the bypass between channels 7 and 8 and also blocking communication between channel 26 and channel 8.

Movement of piston 41 will cause it to expel liquid from cylinder 40. The expelled liquid will first move valve .54 against the resistance of spring 55 and cause it to expel liquid from spring chamber 48 into channel 26 until valve 54 uncovers port 49 and then piston 41 will expel liquid from cylinder 40 through port 49 into channel 26. Since the cross-sectional area of piston 41 is several times that of valve 54, a slight movement of piston 41 will result in a substantial movement of piston 54 so that port 49 is uncovered very. quickly. Also, movement of valve 54 away from its neutral position causes it to block port 51 and thereby block communication between channel 26 and channels 7 and 8.

As soon as slideblock 35 ceases to move, spring 55 will be able to return valve 54 to its neutral position be cause the same pressure prevails at both ends of the valve. The return movement of valve 54 causes it to eject liquid from the inner end of bore 47 and the ejected liquid will flow directly through port 49 into channel 26 until valve 54 blocks port 49 and then the ejected liquid will flow through groove 56 and port 49 into channel 26. s

- covers port 49 and to table 1 and pump P1 must create in the pressure side 6 2-6 to gradually accelerate table 7 of slideblock 35 ceases, valve When slideblock 35 is in its neutral position and cylinder 37 is connected to exhaust, the control pressure in cylinder 40 will cause piston 41 to move slideblock 35 downward in respect to Fig. 4 and liquid will flow into spring chamber 48 and cause valve 54 to move toward cylinder 40 and maintain the pressure therein until valve 54 partly uncovers port 49 and then liquid will flow from channel 26 through ports 49 and 50 and channel 53 in cylinder 40 and keep piston 41 and slideblock 35 moving until the escape of liquid from cylinder 37 ceases. Movement of valve 54 away from its neutral position causes it to block port 52 :and thereby block cordnrgunication between channel 26 and channels 7 an Movement of slideblock 35 downward in respect to Fig. 4 will cause pump P1 to discharge liquid into channel 7 and, with valve 9 in the position shown in Fig. 1, the liquid discharged cylinder 3 and cause ram 6 to right on a cutting stroke. Spring 68 will cause valve 67 to move with piston 41 and to block communication between ports 61 and 62 so that no liquid can escape from channel 7 into channel 65.

The rate at which pump P1 discharges liquid will gradually increase from zero as slideblock 35 moves away from its neutral position, thereby causing motor move table 1 towardthe slideblock 35 ceases at which time table 1 will be moving at a predetermined cutting speed.

During acceleration of table 1, valve 54 will keep the main circuits locked by blocking port 52 so that all liquid discharged by motor 26 must be returned to pump P1 and the only back pressure on motor 2-6 is the supercharge pressure which is determined by the adjustment of relief valve 29. But as soon as movement 54 will be returned to 55 and will permit the to extend into motor 2-6. 54 toward its neutral position will from channel 26 through ports 49 53 into cylinder 40 until valve 54 then to flow through port 49 and cylinder 40 to maintain the control pres its neutral position by spring back pressure in channel 26 Movement of valve cause liquid to flow and 50 and channel groove 56 into sure therein.

At about the time that table 1 reaches cutting speed,

a stationary tool starts to take a cut from work fastened of the circuit a pressure which exceeds the back pressure by an amount sufficient to enable motor 26 to overand the resistance of the work to the action of the tool thereon, thereby causing the liquid in the pressure side of the circuit to be compressed. However, the tool resistance will vary due to variations in the thickness and hardness of the work.

Whenever there is a sudden and considerable decrease in tool resistance, such as when. the tool breaks out of the work during one part of a cut, the compressed liquid in the pressure side of the circuit will expand and cause the table to jump forward which will cause the pressure in the pressure side of the circuit to drop momentarily. locked or completely closed, the forward jump of the table would cause the liquid in the return side of the circuit to be compressed and at the end of the jump the compressed liquid in the return side of the circuit would expand and cause the table to chatter. But by having the circuit unlocked as explained above, the forward jump of the table will cause a small volume of liquid to be expelled through the back pressure relief valve which has been indicated in Fig. 1 as being valve 27 but which in practice is the relief valve of the third pump. By maintaining a relative high back pressure on the motor and providing a back pressure relief valve, the effect of variations in tool resistance is minimized and exceptionally smooth operation of the planer is obtained.

Shortly before table 1 reaches the end of a cutting stroke, liquid is supplied to cylinder 37 at a regulated rate and causes piston 38 to move slideblock 35 upwould cause it to overrun and to expel liquid through the back pressure relief valve but, as soon as slideblock 35 starts to move from its preset position, piston 41 will eject liquid from cylinder 40 which will cause valve 1 until movement of If at that time the circuit were to move lnth'e 'safne direetien "and "to tule'c'kjport 51, as prevlpusly explained, urertiy .lockingfthe circuit s'o flra'tthe speedpf ralile 1 is determined by the rate at which the liquid expelled from meter 2 -6 pm enter pump P1 with the "result that table 1 i decelerated at arate 1pm 'ortiona'l to the rate at'v'vhic'hthe displacement of "pump 1 is reduced.

V :Srtdeeloek'aswillontinuefto m'ove andga soon a's it passes beyond "its neutral fpositio'n, "p'ump 'Pl will discharge liq id into channel 8 which 'will cause motor 26 'to movealile 11 toward "the ileft'on a-re'turn stroke. Pump P1 Will discharge liquid into channel 8 at a gradually increasing rate =andcausemotor 2+4? to gradually-accelerate "table -1"'uritil s'lide'b'lock 35 reaches a selected position at 'which time table 1 will be-moving at a;pregletermined return speed and spring-55 will return valve '54 to its neutral position. i A I A l shoitlybfore table 1 reaches the end of the -retur'n stroke cylinder 13 "is c'onnected toexhaustand the liquid supplied to cylinder 40 w1ll shift valve 154 to locl; the circuit and will cause piston 41 to move slideblock 35 downward rin respect to Fig. 4 to thereby first decelerate'table 71 micro speed and -then;accelerate it toa c'uttingrspeed as explained above. Table -1 will continue to reciprocate in the above described manner until stopped bythe-operator. q

Valve 54 thus automatically locks the -circuit at the beginning of each deceleration "of table 1 with the result that the reversal of table 1 at each end of 'its stroke takes ,plac e each time at the same point regardless of how fast the table :is moving during the cutting and return strokes.

CONTROL *FOR MKIN *PUM'P :Liquid fiowsto and fromcylinden37 through a-channel 6'? which connects cylinder 37 'to a valve block 70 containing a valve mechanism which controls the operation-of pump P1. The several tparts of the valve 'mecha nisrn-are arranged close together 'and t the valve ,-:plungers are alongside each other within block =70 but, in 'order 7 to illustrate the relation between the parts and to clearly show the paths through which liquid flows within block 70, the parts have been spaced apart in Fig. v5 and the plunger s shown :in the positions occupied when the slideb loek 35 :is-in its neutraltposition and the1pumps arerunnin T he flow of liquid to a'nd from cylinder -37 is'contro'lled by a pilot valve :plunger V 1 which is moved away frem :a neutral position in response to :movement of "one or both of two plung ers Vt2 and V3 and is moved itoward the ngutral position in response to movement of slidebl'ock 35. Plunger V1 :is moved orlpermitted to be moved by a folloW-up -mechanism shown as including ateeter bar 7 1, which has, its ends pivoted upon upper ends of plungersjVZ and V3, and a floating-lever 7-2 which has one -of -its ends pivoted upon the upper end of plunger V 1 ;and;its other end pivoted to bar 71 intermediate the ends thereof.-

In order to simplify thedrawing, floating lever 72 has been shown as being engaged intermediate its ends by one end ofa rod 7 3 the other'end'of which engages piston 38 but in pract-ige slideblock 35 :is arranged horizonand lever isengaged intermediate its ends by one end of'a s'uitable linkage the other end of which is fixed to or gigages slideblock 35 at a .-point remote from cylinder Pilot valve plunger V1 has three spaced apart heads or {pistons 74, 75 and 76 formed-thereon and fitted in a bore 77 which is formed in valve block 70 and has formed in the wall t' hereof an annular groove or port 73 to which channel 69 is connected. Piston 75 controls communication between port 7 8 and a branch of chair nel "26, which communicates with bore 7;? above piston 75, and between por't 78 and an exhaust 79 which communica t'e's with bore 77 below piston 75. When plunger V1 "is :in its neutralpositiongport 78 {is covered by piston 75 whidh fha's beenjs ho'w'has being of the same width as port 78 w; it may-bewtdemhm ,po'rt'78 and have slots fenned in its edges ccording to common practice. A small diameter bore 80 extends from "the lower end of plunger V1 upward be ond iston 75 and then extends radially entward into communication with b'ore'77. A plunger s1 is rnt'edin boreso andre'aets against the lower end wall of bore 70.

tallglplungers V1, V2 and V3 are arranged verticallyv arrangement is;such that 'the contfrol :pr essure extends from channel 26 -into bore 150 and urges plunger V1 upward against the letgt end ofglever 7 2 and thereby causes lever 72 t o-hold rod 73agai rrstrpiston-38 When the right end of lever 72 is raised due -to upward'move ment of one or both of .plungers 1V2 andyii, lever 72 will pivot upon rod 73 -and Tracie-plunger Vl dqwnward. Then liquid will 'fiow frofn channel 26 through bore 77 port 78 and cha nnel'62 'to cylinder 37 'andcausepis'ton 38 to move slideback 35 upward in -respect to the drawing. The pressure in bore 8Q will tend to move Iplunger V1 upward as 'fast as lever 72 tends to move -it downward with the result that plunger V1 isreturnedjto 1neutral and stops further movement of slideblock 35 substantially as soon-as movement'of the right end of levcr n r a Whenone or bpth oj plungers V2 and V3 are moved downward, lever -72 yvill apivot upon rod 73 and (permit the pressure in bore to move gplung'er V1 upward-to connect port 78 to -exhaust .port 79, thereby reducing :the pressure in cylinder -;37 and permitting servo-motor 40 41 to move slideblock 35 downward iniresp'ect to the drawing as previously explained. Piston 38 will eject liquid from cylinder 37 through channel 69 ;bore'70'an'd port 79 to exhaust. Rod 73 will rnove withslideblock 35 and will tend to moye the leftend of lever 72 downward as fast as the right end thereof moves downward so thattplunger V 1 is ret-urn'ed to its'neutral position and stops further movement of slideblock 35 substantially as soon as movement of the rightend-ofdever 72 ceases.

Plunger-s V1, V2;and V3 are :urged upward hydraulically and, in order that -they may exert only small =forces upon the follow; up mechanism, the control pressure acts upon only afsrnall area of :plunger Vl and liquid for urgingplungers V2 and V3 is supplied the'retoa't a-low value such asc4O .-p. 's. i. v

As shown, a pressure reducing valve V-havi'n'g :three spaced ;a art heads or vpistons 84, and 86 is fitted "in a bore 8 which is formed in valve block -70 and has an annular groove or port 88 formed in;its wall and conne cted to a branched supplychannel-89. -Piston 85 c0ntrols communicatigin between port 158 and a branch of control channel 26, which communicates with bore 87 above port 88, and between ,port 88 ,and an exhaust port 90 which communicates with bore '87 at a point below port88. Valve V4 is urged downward by a spring .91 and it is urged-upward by liquid supplied'to the lower end of bore-8 7 from port 88through a passage 92 which extends radially :into vpiston 85 and then extends downward through the-lower: end of valve V4. V

The arrangement is suchfthat spring 91I=will initially hold valve V4 against the lower end wall of bore '87 b s oon as pump P2 is started, liquid will flow through channel 26, here 87 and passage 92 into the lower end of bore 87 -and will raise valve V4 against the resistance of spring-9 1;. If 'too great-a pressure has been created in channel 89 before valve V4 closes port 88, liquid will floyv through passage 92 to the lower end of 'bore 87 and will raise valve V4 until enough liquid has escaped from channel-89 to drop the pressure in channel -89 to the pressure determined by the resistance of spring 91. Thereafter, variations in the flow of liquid through channel 89 will c'ausejvalve V4 to move downward and upward alternately -and thereby maintain the pressure in channel 89 at :a substantially constant value.

H The direction in which table 1 will move when started from a stationary position is determined by a directional valve V5 having three spaced apart heads or pistons 95, 96 and 97 formed thereon and fitted in a bore 98 which isformed in valve block 70 and communicates at its opposite ends with two spring chambers'99 and 100'o'f greater diameter yalve V5 is spring centered by two springs,101 and 102 :and two spring retainers 103 and 104. Spring 101 normally holds spring retainer 103 against the end of spring chamber 99 and against the outer face of "piston 95, ahd spring 10 2 normally holds spring retainer I04 against the end of spring chamber 100 and against the outer 'face of piston 97.

'Piston 96 controls communication between annular groove or port 105, which is forni'e'clin the wall of bore 98 and has a channel 106 connected thereto, and supply channel 89 to abra'nc'h of which communicates with bore 98 at a'po'i'iit *between pistons '95 and'9l5. Piston 976 also controls communication between port and a passage 107 which extends radially into valve V4 between pistons 96 and 97 and then extends axially downward through the lower end ofvalve V4 so that the space between pistons 96 and 97 i: open at all times to spring chamber 100 which is open to exhaust such as by means of a port 108 formed in the lower wall of chamber 100.

Movement of valve V in one direction or the other is effected by one or the other of two solenoids 109 and 110 shown as being connected to opposite ends of a lever 111 which is pivoted intermediate its ends upon a stationary bracket 112 and has one of its ends connected to the stem of valve V5.

The arrangement is such that solenoid 109 when energized will move valve V5 downward and then liquid can flow from channel 89 through bore 98 and port 105 into channel 106 and, when solenoid 109 is deenergized and solenoid 110 is energized, valve V5 will be moved upward and permit liquid to escape from channel 106 through port 105, bore 98, passage 107, spring chamber 100 and port 108 to exhaust.

The other end of channel 106 communicates with an annular groove or port 117 formed in the wall of a bore 118 which is formed in valve block 70 and has a second annular groove or port 119 formed in its wall and connected with one end of a channel 120. Port 117 also communicates with one end of a channel 121 having a choke 122 connected therein, and a third channel 123 having a choke 124 connected therein communicates with bore 118 between ports 117 and 119. Communication between channel 123 and ports 117 and 119 is controlled by a slow speed valve V6 which is fitted in bore 118. Valve V6 is urged into its upper position by a spring 125 and is adapted to be moved into its lower position by a solenoid 126. Movement of valve V6 into its lower position will cause slow speed plunger V2 to move in one direction or the other in response to valve V5 being moved in one direction or the other.

Slow speed plunger V2 has three spaced apart heads or pistons 130, 131 and 132 formed thereon and closely fitted in a bore 133 which is formed in valve block 70. Piston 131 normally covers an annular groove or port 134 which is formed in the wall of bore 133 and has channel 120 connected thereto. Two branches of supply channel 89 communicate with bore 133 at opposite sides of piston 30, channel 123 communicates with bore 133 below piston 132, and an axhaust port 135 communicates with bore 133 between pistons 131 and 132. Piston 131 is so constructed, such as being the same width as port 134, that a slight movement thereof will uncover a portion of port 134.

The arrangement is such that, when the displacement of pump P1 is zero and pump P2 is running, the pressure in the upper end of bore 133 tends to move plunger V2 downward but it cannot do so because liquid is trapped in the lower end of bore 133 by valve V6. If liquid should escape from the lower end of bore 133 and permit plunger V2 to move downward, piston 131 would uncover a portion of port 134 and permit liquid to flow from channel 89 through bore 133, port 134, channel 120, bore 118 and channel 123 to the lower end of bore 133 and move plunger V2 upward until piston 131 closed port 134 which would stop further upward movement of plunger Reversing plunger V3 has two spaced apart heads or pistons 140 and 141 formed thereon and fitted in a bore 142 which is formed in valve block 70 and has a branch of supply channel 89 communicating with its upper end. Bore 142 has two annular grooves or ports 143 and 144 formed in the wall thereof and communicating, respectively, with two channels 145 and 146 through which liquid may flow to and from bore 142. Ports 143 and 144 are so located that the adjacent ends of pistons 140 and 141 aline with adjacent edges of ports 143 and 144 when plunger V3 is in its neutral position but the distance between the adjacent edges of pistons 140 and 141 may be very slightly greater than the distance between the adjacent edges of ports 143 and 144 in which case liquid will seep from one port to the other when plunger V3 is in its neutral position and there is pressure in one of the ports.

Plunger V3 has a passage 147 extending into it from its lower end and then extending radially outward between pistons 140 and 141 to permit flow of liquid between the lower end of bore 142 and one or the other of ports 143 and 144 when plunger V3 is shifted in one direction or the other from its neutral position. Passage 147 com- 163 and 165 which municates at its upper end :with a passage 148 which extends upward through plunger V3 and communicates with the upper end of bore 142 through a hole 149. The upper end of passage 148 is closed by a stem 150 which is threaded into the upper end of plunger V3 and ex tends upward through the bifurcated end of teeter bar 71. Passage 148 has arranged therein a check valve 151 which prevents flow of liquid from the upper end of bore 142 into the lower end thereof but permits flow of liquid from the lower end of bore 142 into the upper end thereof at the instant that plunger V3 substantially covers ports 143 and 144 during its downward movement.

It has previously been explained that movement of plunger V3 in one direction or the other will elfect an increase or a decrease in the displacement of pump P1 and thereby accelerate or decelerate table 1. The rate at which table 1 is accelerated or decelerated is proportional to the rate at which plunger V3 is moved but the ac-; celeration rate should not be the same when motor 26 is operating in the high speed range as when it is operating in the intermediate or the low speed range.

Selection between the rates at which plunger V3 may be moved is made by a valve V7 having three spaced apart heads or pistons 155, 156 and 157 formed thereon and fitted in a bore 158 which is formed in valveblock 70. and has four annular grooves or ports 159, 160, 161 and 162 formed in its wall. Valve V7 is urged to its upper position by a spring 167 and it is adapted to be moved into its lower position by a solenoid 168.

Ports 159 and 160 are connected through two chokes 163 and 164, respectively, to channel 145 and ports 161 and 162 are connected through two chokes 165 and 166,. respectively, to channel 146. When selector valve 9 is adjusted to cause motor 2-6 to operate in the high speed range as shown, valve V7 is in its upper position and liquid may flow to and from plunger V3 through chokes regulate the rate at which plunger V3 will move away from its neutral position and thereby regulate the rate at which table 1 is accelerated at each end of its stroke. When valve 9 is adjusted to cause motor 2-6 to operate in either the intermediate or the low speed range, valve V7 will be shifted into its lower -a check valve 186 position and then liquid may flow to and from plunger V3 through chokes 164 and 166 which regulate the rate at which plunger position and thereby is accelerated at each Channels and 146 are adapted to be connected to pressure and to exhaust selectively under the control of a high speed valve V8 which is fitted in a bore 175 formed in valve block 70. Valve V8 is urged to its upper position by a spring 176 and it is adapted to be moved into its lower position by a solenoid 177.

Bore 175 has formed in the Wall thereof an annular groove or port 178, to whichsupply channel 89 is connectecl, and two ports 179 and 180 which are arranged on opposite sides of port 178 and are connected to exhaust. In order to avoid complicating the view, no channels have been shown connected to ports 179 and 180 nor to the port 79 of pilot valve V1 so that those ports appear to exhaust to the atmosphere but in practice those ports exhaust into the liquid in a reservoir which is higher than those ports so that they are kept filled with liquid.

Bore 175 is connected at a point between ports 178 and 179 to bore 158 at a point between ports 159 and by a channel 181 which is connected intermediate its ends to channel 145 by a channel 182 having arranged therein a check valve 183 which permits liquid to flow from channel 145 through channel 182 to channel 181 but prevents fiow from channel 181 to channel 145 except through one or the other of chokes 163 and 164. Bore is connectedat a point between ports 178 and to bore 158 at a point between ports 161 and 162 by a channel 184 which is connected intermediate its ends to channel 146 by a channel 185 having arranged therein which permits liquid to flow from channel 184 through channel 185 to channel 146 but prevents flow from channel 146 to channel 184 except through one or the other of chokes 165 and 166.

V3 will move away from its neutral end of its stroke.

If when the drive is idle plunger V3 should move downward below its central or neutral position, pump.

regulate the rate at which table 1 port 144 which would stop further 'flow of liquid into the lower end of bore 142 and further upward movement of plunger V3. Ifphmger V3 should 'be raised above its central or neutral position, liquid will flow from channel 189 into the upper end of bore 142 and cause plunger V3 to move downward and to e'jectjliquid'from the lower-end of bore 142 through :passage ;147-, port 143 and channels 145, 182 and 18*1andpast valve -80 to exhaust until further downward movement of plunger V3 is stopped by piston 140 covering .port 143 to step further escape of liquid from the lower end of bore 142. Plunger is thus self-centering when valve V8 -is in its uppcrposit-ion.

In order to start table 1 moving from a stationary position plunger V3 is moved slightly off center hy'- draulically but, during normal operation of the drive, plunger V3 is moved slightly beyond center by an overriding control which is operated by two dogs 190 and 191 fastened to'table 1 in such positions that one or the other of the dogs engage the over-riding control as table 1 approaches the end of its stroke in-either direction.

The over-riding control is quite complicated due to it also effecting operation of the auxiliary mechanism of the planer (not shown) and due .to the relative locatlons of table -1 and valve block 70. Since no part of the "invention resides in the over-riding control .per se andin order to avoid complicating the view, the over-riding control has been represented by a simple device including a lever 192 which is pivoted intermediate its ends upon a stationary bracket 193 and has one of its ends bifurcated and pivoted to the stem 150 of plunger V3. The other end of lever 192 carries a roller 194 which is arranged in the paths of dogs 190 and 191 so that, when table 51 approaches the end of the stroke toward the right,

dog 190 will depress roller 194 and cause lever 192 to raise plunger V3 and, when table 1 approaches the endof its stroke toward the left, do'g 191 will raise roller 194 and 'cause lever 192-todepress plunger V3.

When table 1 is reciprocatcd, valve V8 is in 1ts lower position and "movement of plunger V3 beyond its central or neutral rpositionswill cause it to be moved hydraulically to the limit'of its movement in the same direction as will;p'resently' be explained. A

From the foregoing, it will be obvious that movement of plunger V3 in one direction or the other will cause slideblock 35 of pump P1 to be moved in one direction or the other to vary ipump displacement and that the distwice that plunger V3 is moved away from its :neutral position will determine the displacement of pump P1 and thereby "determine the speed at which table 1 will be moved. 1

Upward movement of plunger V3 islimitedby the upper end of stem 150 engaging a stop 195 'shown as being an adjusting screw threaded in a stationary bracket 196. Adjustment'of stop 195 determines the return speed of table 1'. Downward movement of plunger V3 is limited by lever 192 engaging a suitable stop, such .as a cam 197,.which is fixed upon ashaft 198.

The angular position of earn 197 determined the cutting speed of table 1. When'th'e widest part'of 197 is upward, pump P1 can be adjusted to a minimum displacementandfwhenthe narrowest i'partof cam "197 is upward, pump P1 can be adjusted to a maximum displace- I'neht.

Shaft 1-98 ;is connected to a geared cap'a citator motor M2 '(Fig. 10) which is adapted to rotate shaft 198 and cam 197 in either direction selectively iinder the control df' t'he'operator. In'or'der to prevent cam 197 from being rotated beyond either its'maxi'rrium displacement position or its minimum displacement position, a'cam 199 is fixed upon 's'haft198 and two normally closed limit switches LS2 and LS3 are'conn'ected in series with motor M2 and are so located that switch LS2 will beo'pened by :cam 199 in response to cam '197approaching its maximum displacement position and switch LS3 will be opened by earn 199 in response to earn 197 approaching itsmin'ir'num displacement position. I I

In order to indicate "to the operator the speed at which table 1 will r'noveon'a cutting stroke, a gage graduated in feetjper minute for each of the three speed'ranges may be arranged at the operators station and electric current for operating the g-ag'e' may be supplied thereto through an electric pi'ck-fup '200 (Fig. 10 lhaving'the'ste'm-cf its core in centa'ctwith a eam 201 which is fixed upon shaft 198 and has the same contour as cam 197. The flow of cur- 12 rent through the pick-up will vary in response to movement of the pick-up core. Since the contour of earn 201 is the same as that of cam 197 and since the position of slideblock 35 and consequently the speed of table 1 is determined by the angular position of cam 197 the gage will indicatethe speed of table 1. Since position indicating means of this type are well known and in commercial use, only the .pick-upand the cam have been illustrated.

THE ELECTRIC CIRCUIT As indicated in Pig, 7, electric current for energizing motor M 1 is suppliedfrom ;a power source through a line switch S1 to three power lines L1, L2 and L3. Preferably, motor M2 and solenoids 109,110, 126, 1'68 and 177 are connected into a control circuit to which current is supplied at a voltage lower than the voltage in the power line.

-As shown, current is; supplied to the control circuit through a transformer .210 which has opposite ends of its primary connected to iines L2 and L3 respectively, one end of its secondary connected to :one side L4 of a -control circuit and the other end of its secondary connected to the second sideLS of the control circuit through a normal-lyopen starting switch SS1 and a normally-closed stop switch SS2. In order that the [planar table may be stopped without interfering with other functions of the control,the second side of the control circuit hasa branch line L6 which .-is connected to -line L5 through a normally closed stop switch SS3.

Motor M1 is controlled by a magnetic motor starter switch which, in order to avoid complicating the drawing, has been represented by a simple contactor C1. Solenoids 110, 109, 126, 177 and l68 are controlled by magnetic switches or cont'actors-CZ, C3,- C4, C5 and C6 respectively. As indicated schematically in Fig. 8, motor starter C1 and contactor C4 each has four normally'open switches a, b, c and-d and a magnet for closing the switches. Each of the contactors C2 and C3 has three normally open switches a, -b and c, a normally closed switchd and a rnagnet m for operating the switches. Each o'f'contactors C-5 and G6 has two normallyopen switches a and b and a magnet-m forclo'sing' the switches.

Motor starter 01 has its magnet 61" connected between lines L4 and L5, its switch C 1 connected in :parallel with starting switch-SS1 9, and its switches C1 C1 :and C1 connected between motor M1 and -lines L1, L2 and L3 respectively. When line switch S1 is closed, closing starting switch SS1 will cause current to flow in the:eontrol circuit to energize magnet 01 which will close the mo tor starter switches. Switch C1 will keep :current flowing in the control circuit and thereby :keep inagnet C1 energized when switch SS1 is released. Switches "C1 C-1and C1 willcstablisha circuit through motor M1 to energize it. Motor M1 will then continue'to run until stop switch SS2 or line *switch S1 is 'opened.

Solenoids 110, 109, 126, 177 'and 168, which operate the valves sh'o'wn in -Fig'. -5,-have'the-opposite ends of their windings connected to lines L4 and 'LS' through the switches a and b of contactors C2, C3, C4, C5 and respectively. That is, solenoid has one end of its winding connected to one contact'cf switch C2 ,'theother end -'-of its winding connected to 'one contact of switch 7 C2 and the other contact :of switches 02 and C2 are connected to linfes L4 and L5 respectively. The'otherfour solenoids are similarly connected "to lines L4 and L5 through switches 03 and C3 C14 and C4 C5 and C5 and C6 and-C6 respectively.

Motor M2 has one of its terminals connected to line L4 and its other two terminals connected to line L5 through limit-switches 'LSZ and LS3, respectively, and two pushbut-ton starting switches SS4 and SS5 =eachof which has been represented in Fig. 7 bya double acting pushbutton switch having an upper normally closed contact -a and a lower normally open c'ontactb.

The arrangement -is such that, when s'witc'h SS4 is 'depressed, itlwill establishacircnit (=L4 MZ -LS24SSS SS4 L5) to cause motor M2 to rotate shaft 198 and cam --19=7 (Fig. 7) in a direction to'effect an increase in the displacementofrpunip =Pq1. Elf-switch SS4 is depressed for too long a time, cam 199 will open switch LS2 and stop motor .M2before cam 4.97 has been rotated beyond ts maxim-um displacement position. Whcns'wit'chSSS is; depressed, it will establish acircuit L4=:M-2*-LS3== SS5 SS4 'L5) to cause motor M2 to rotate shaft 198 and cam 197 in a direction to eflect a decrease in the displacement of pump P1. If switch SS5 is depressed for too long a time, cam 199 will open switch LS3 and stop motor M2 before cam 197 has been rotated beyond its minimum displacement position. The reason for using double acting switches is to prevent motor M2 from being energized if the operator should depress both switches SS4 and SS5 at the same time.

Magnets C2 and C3 of contactor C2 and C3 have the winding of each connected at one end to line L4 and connected at the other end to branch line L6 through two double acting starting switches SS6 and SS7 each of which has a normally closed upper contact a and a normally open lower contact b. Switches SS6 and SS7 preferably are double acting as shown to prevent both of magnets C2 and C3 from being energized at the same time.

Thearrangernent is such that depressing switch SS6 will establish a circuit (L4C2 -SS7 -SS6 L6) to energize magnet C2 which will cause contactor C2 to close its switches and effect energization of solenoid 110 and depressing switch SS7 will establish a circuit (L4- C3 -SS7 -SS6 -L6) to energize magnet C3 which will cause contactor C3 to close its switches and effect energization of solenoid 109.

Magnet C4 of contactor C4 has one end of its winding connected to line L4 and the other end of its winding connectable to line L6 through either switch C2 or switch C3 or through. switch C4 and a manual switch S2 which selects between manual control and automatic op eration of table 1. Switches C2, C3 and C4 are connected in parallel with each other and switch S2 1s connected in series with switch C4".

The arrangement is such that, when contactor C2 or C3 is operated in response to switch SS6 or SS7 being depressed, the switch C2 or C3 thereof will establish a circuit through magnet C4 which will cause contactor C4 to close its switches. If selector switch S2 is open, contactor C4 will return to its normal position when the depressed switch SS6 or SS7 is released. But if selector switch S2 is closed, operation of contactor C4 will cause its switch C4 to establish a holding circuit to .keep magnet C4 energized and contactor C4 operated when the depressed switch SS6 or SS7 is released.

Magnet C5 of contactor C5 has one end of 1ts winding connected to line L4 and the other end of its winding connected to line L6 through switches C2 C4 and C3 When contactor C4 first operates and closes its switch C4 switch C2 or C3 is open so that magnet C5 of contactor C5 will not be energized until the depressed switch SS6 or SS7 is released and permits the operated contactor C2 or C3 to return to its normal position and close its switch C2 or C3 which will establish a circuit through magnet C5 Magnet C6 of contactor C6 has one end of its wlndlng connected to line L4 and the other end of its winding connected to line L5 through normally open limit switch LS1 so that contactor C6 will be operated whenever switch L S1 is closed in response to speed range selector valve 9 (F g. 1) being shifted into its low speed range position or 1ts intermediate speed range position.

OPERATION Assuming that line switch S1 has been closed, that starting switch SS1 has been closed momentarily to cause motor starter C1 to close and start motor M1, that cam 197 (Fig. 5) has been adjusted to obtain the desired speed of table 1, that the displacement of pump P1 is zero and that selector valve 9 is in the position shown in Fig. l, the drive will operate as follows:

Slow speed operation If it is desired to start table 1 moving toward the right or in a cut direction, depressing starting switch SS6 (Fig. 7) will establish a circuit to energize magnet C2 which will cause switches C2, C2 and C2 to close and switch C2 to open. Closing switches C2 and C2 will establish a circuit to energize solenoid 110 which will raise directional valve V5 (Fig. 5). Opening switch C2 will prevent magnet C5 from being energized when switch C4 closes. Closing switch C2 will establish a circuit to energize magnet C4 which will cause switches C4, C4 C4 and C4 to close. Closing switches C4 and C4 will establish a circuit to energize solenoid 126 which will move valve V6 downward into the position shown in Fig. 6. Closing switch C4 will have no effect if selector switch S2 is open. Closing switch C4 will have no effect at this time because switch C2 is open.

Moving valve V5 upward and valve V6 downward destroys the pressures in the lower ends of bores 133 and 142 which permits liquid to flow from channel 89 into the upper ends of bores 133 and 142 and cause plungers V2 and V3 to move downward and to eject liquid from the lower ends of bores 133 and 142 through channels 123 and 121, respectively, into bore 118 and then through channel 106, bore 98, passage 107, chamber 100 and port 108 to exhaust. Plunger V2 will move downward to the limit of its movement at a rate determined by the t to open its switches C2 lever 72 to pivot upon rod 73 gize magnet C4 limited rate at which it can eject liquid through the choke 124 in channel 123.

As soon as plunger V3 starts to move downward, it uncovers a very small portion of port 144 and then liquid will flow from channel 89 through bore 175, channels 184, 185 and 146, port 144, passage 147, the lower end of bore 142 and the previously described channels to exhaust but choke 122 will restrict the flow of liquid therethrough and cause creation in the lower end of bore 142 of a pressure which is sufiicient to support plunger V3 and which is only about one-half the pressure in channel 89 because the area of the about twice the area of the upper end of piston 140. Plunger V3 will move downward so little that the effect of its movement upon the be negligible.

Movement of plunger V2 to its lower position permits the left end of teeter bar 71 and the right end of lever 72 to descend and thereby permit the pressure in bore 80 to move plunger V1 upward and connect servo-motor cylinder 37 to exhaust. Then the liquid continuously supplied to servo-motor cylinder 40 (Fig. -4) will cause piston 41 to move slideblock 35 in a direction to cause pump P1 to discharge liquid into channel 7. Rod 73 will move with slideblock 35 and will cause lever 72 to return plunger V1 to its neutral position and stop further move ment of slideblock 35 when slideblock 35 has been moved a dlstance substantially proportional to the distance that plunger V2 is moved. At that time, pump P1 will be discharging liquid into channel 7 at a limited rate which will cause motor 2-6 to drive table 1 toward the right at a slow speed.

When starting switch SS6 (Fig. 7) is released), it will deenergize magnet C2 which will permit contactor C2 C2 and C2 and to close its switch C2. Opening switches C2 and C2 will deenergize solenoid which will permit valve V5 to be returned to its neutral position by its spring 101. With selector switch S2 open, opening switch C2 will deenerwhich will open its switches C4, C4, C4 and C4 Closing switch C2 has no effect because switch C4 is open. Opening switches C4 and C4 deenergizes solenoid 126 which permits valve V6 to be returned to its initial position by spring 125. Opening switches C4 and C4 has no effect at this time.

With valves V5 and V6 in their normal positions, no liquid can escape from the lower ends of bores 133 and 142. The liquid flowing from channel 146 through port 144 through passage 147 into the lower end of bore 142 will raise plunger V3 until piston 141 covers port 144 at which time plunger V3 will be in its normal position. At the same time, liquid will flow from channel 89 through bore 133, port 134, channel channel 123 to the lower end of bore 133 and will raise plunger V2 at the rate determined by choke 124 until piston 131 covers port 134 at which time plunger V2 will be in its normal position.

The left end of teeter bar 71 lever 72 will move upward with displacement of pump P1 will and the right end of plunger V2 and cause and depress plunger V1. Then liquid will flow from channel 26 through bore 77, port 78 and channel 69 to cylinder 37 and cause piston 38 to move slideblock 35 toward its neutral position. Rod 73 will move with slideblock 35 and permit the left end of lever 72 to move upward with the right end thereof until the pressure in bore 80 has returned plunger V1 to its neutral position to stop further flow of liquid into cylinder 37 at which time slideblock 35 will be .in its neutral position and movement of table 1. will cease.

If it is desired to start table 1 moving toward the left or in a return direction, depressing starting switch SS7 will establish a circuit to energize magnet C3 which will cause switches C3 03 and C3 to close and switch lower end of piston 141 is 120, bore 188 and C3 to open. Closing switches C3 and C3 will establish a rcireuit to energize solenoid 109 which will move directional valve V downward. Opening switch C3 will prevent magnet C5 from being energized when switch C4 closes. Closing switch C3 will establish a circuit to energize magnet C4 which will cause switches C4 C4 C4 and C4" to close. Closing switches C4 and Cd establishes a circuit to energize solenoid 126 which will move valve V6 downward into the position shown in Fig. 6. Closing switch -C4 will have no effect if selector switch S2 is open. Closing switch C4 will have no effect at this time because switch C3 isopen.

Moving valve V5 downward permits liquid to flow from channel 89 through bore 98, channel 106, port v117 and channel 121 to the lower end of bore 142 and raise plunger V3 until it uncovers just enough of port 143 to permit liquid to flow from the lower end of bore 142 through passage 147, port 143,.channels 145, 182 and 181, bore 175 and port 179 to exhaust at the very limited rate at which the liquid can flow through choke 122. Plunger V3 is raised so little that its effect upon the displacement of pump P1 is negligible.

Moving valve V6 downward into the position shown in Fig. 6 permits liquid to flow from channel 106 through :bore 118 and channel 123 into the lower end of bore 133 and move plunger V2 upward to the end of its stroke at a rate determined by the rate at which the liquid can flow through choke 124.

The left end'of teeter bar 71 and the -right:end of lever 72 will move upward with plunger V2 and cause lever 72 to .pivot upon rod 73 and depress plunger V1. Then liquid will flow from channel 26 through bore 77 port-'78 and'channel 69 to cylinder 37 and cause piston 38 to move slideblo'ck 35 inadirectio'nto cause pump P1 to discharge liquid into channel 8. Rod 73 will move with s'lide'bloc'k 35 and will cause lever 72 to return plunger V1 to its neut'ral position and stop further movement of 'slideblock 35 when slirleblock 35 has been moved a distance substantially proportional to the distance that plunger V2 was moved. At that time p'ump Pd will be discharging liquid into channel 8 at a limited "rate which will cause motor 2-6 to drive table 1 toward the left at a slow speed.

'When starting switch S87 is released, it will dee'n'er gize magnet C3 which will permit contact C3 to open its switches CFs B CB and C3 and to close its switch C3. Opening switches C3 and C3 will 'deenergize solenoid 109 which will permit valve V5 to be returned to its neutral position by spring 102. With selector switch S2 open, opening switch C3 will defenergize magnet C4 which will open-its switches C4,-C4, C4 and Ol Clos- Will have no effect because switch C4 is open. O pening switches "04 and C4? will deenergize solenoid 126 which will permit valve V6 to be returned to its initial positio'nby spring 125. Opening-switches (24 and C4 has no effect at this time. V

Returni'ng valve V5 to-its normal position cuts ofi flow of liquid to the lower-end of bore 142 "and permits thep're'ssure in the upper end of bore 1'42 to cause plunger V3 to move downward and to eject liquid from the lower end of'bore' 142 through passage 147, port 143, channels 1 45, 182'an'd 18 1, here 175 and *port 179 to exhaust until 15151011140 covers'po'r't143 and'traps the remaining liqui'd inthe lower endof bore 142, thereby causing plunger V3 to stop in its neutral position. Thus, when valve V3 is in its normal position, plunger V3 will center itself regardless of the direction in which it has been moved away from center.

Returning valves V5 and V6 to their neutral position destroys "thepre's'sure in the'lower end of bore 133 and permits the pressure in the upper-end of'bore 133 to-ca'use plunger V2 to move downward and to eject liquid from the lower end of bore 133 through channel 123, bore 1 18, channel 129 and ports 134 and 135 to exhaust until piston "131 blocks port 134 at which time plunger V2 is in its neutral position.

Downward rnovem'ent of plunger V2 permits the left end "of teeter bar 71 and the right end of lever '72 to descend and thereby perm'it the pressure in bore 80 to moveplunge'r 'V1 upward a'nd connect serv'o motor cylinder 37 'to 'exhaust. T hen theliquid continuously supplied to cylihder'40 'will'cause piston 41 to move slideblo'ck 35 toward itsheutral position. Rod-73 will-movewith slidebl'ock 55 and will return tplunger V2 to .its neutral position and stop further movement of slideblock 35 substantially as soon as movement of plunger V2 ceases at which time slideblock 35 will be in its neutral position as move- When it is desired that table 1 shall reciprocate continuously until stopped by the operator, selector switch S2 is closed. Table 1 may be started moving in either direction by depressing starting switch SS5 or SS6 to ef fect opera-non of contactor C2 or C3 and thereby cause contactor C4 to-close its switches 04*, C4 04 and C4 as explained above.

Closing switches C4 and C4 will establish a circuit to energlze solenoid 1 26 which will move valve V6 downward mto the position shown in Fig. 6. With switch S2 closed, closing swltch C4 will establish a holding circuit through magnet C4 Closing switch-C4 will close one gap in the crrcuit through magnet C5 of contactor C5. Table 1 will move at slow speed as -long as the starting swltch is held down as explained above.

When the depressed starting switch is released, it Will deenerglze magnet C2. or C3 and cause the operated contactor C2 v:or C3 to return to its normal position and permit valve V5 :tO return to its normal position as explained above. But the return of contactor C2 or C3 to 1ts normal .position does not cause contactor C4 to return to its normal position because it is held in operated position by the .holding circuit .(L4--C4 S'2'C4--'L6). As contactor C2 or C3 .returns to its normal position, its switch C2 or C3 establishes a circuit to energize magnet 05" and cause contactorCS to close its switches. Closing switches C5 :and C5 established a circuit to energize solenoid 177 which will shift valve V8 into the position shown in Fig. 6.

If valve V8 is shifted downward when .pump P1 is discharging liquid into .channel 8 and causing motor -2-6 to move table 1 toward the'left at a slow speed, plunger V2 will be in its upper position and iplunger V3 will .be sl1ghtly above its .neutral position so that port 143 is slightly uncovered. Shifting valve V8 will causeliquid to flow from-channel 89ipast valve V8 and :through channel 181, .port 159, choke 163, channel .145, .port Y143 :and passage 147 into the lower :end of bore .142 and move plunger V3 upward at a rate determined by the rate -;at which 'the'liquid can flow through choke 163.

Plunger V3 will raise :the right end-of teeter bar '71 and cause lever 72 'to :pivot upon rod 73 and :move plunger V1 downward to permit liquid to flow ifrorn channel 26 through bore 77 and channel 29 to cylinder 37 and move piston 38 and slideblock 35 .in -a direction to cause pump P1 'to increase the rate at which it discharges liquid into channel 8until stern :150 engages stop 5195 at which time movement of slideblock 35 will cease, as previously explained, and pump P1 will be discharging .liquid .into channel 8 at-the rate required to ;enable motor 26 to move table 1 at a speed tdetermined'by fthe adjustment 10f stop 195.

If valve V8 is shifted downward when pump P1 is discharging liquidiinto channel 7 andcausing motor 2-6 to .move table 1 toward the rightat slow speed, .plunger V2 will be :in its lower positionand plunger V3 will be slightly below its neutral position so that port :144 is slightly uncovered. Shifting .valve -V8 will connect .the lower end of .bore 142 .to exhaustand .perrnit liquid to flow from channel 189 vinto the upper end of 'bore 142 and cause plunger V3 to move downward and to eject liquid from the lower end of bore .142 through passage 147, port 144, channel 146, choke 165, port 161, channel 184 and port 182 to exhaust. Plunger V3 will move downward at a rate-determined by-the 'rate at which the liquid-can flow through choke -16'5.

Downward movement of plunger V3 'will permit the pressure in bore 80 to-raisegplunger V1 which will iconnect cylinder 37 to exhaust and permit servo-motor 40'41 -to-move slidcblock 35in a directiontocausepump P1 to increase "the =rate at which it discharges liquid into channel .7 until lever =192 engagesstop 197 at whichltirne movement "of slideblock :35 will cease, as previously explained :and pump 1P1 .will 'be discharging liquid into channel '7 at the'rate required to enable motor 2-6 to move table -:1-'at-a speed determined .by theiadjustment of stop Table 1 will move toward the right at the speed determined by the adjustment of cam 197 until dog en- .71 and cause lever 72 to move 17 gages roller 194 and causes lever 192 to gradually raise plunger V3 which will raise the right end of teeter-bar plunger V1 downward which will permit liquid to flow to cylinder 37 and cause piston 38 to move slideblock 35 upward in respect to Fig. 5, thereby reducing the displacement of pump P1 and decelerating table 1.

Dog 190 will cause lever 192 to raise plunger V3 until piston 140 uncovers a small portion of port 143, at which time slideblock 35 will be approximately in its neutral position and the speed of table 1 will be approximately zero, and then liquid will flow from channel 89 through bore 175, channel 181, port 159, choke 163, channel 145, port 143 and passage 147 into the lower end of bore 142 and will move plunger V3 upward at a rate proportional to the rate at which the liquid can flow through choke 163. At the same time, liquid will. flow from the lower end of bore 142 through channel 121, bore 118 and channel 123 into the lower end of bore 133 and move plunger V2 into its upper position.

Upward movement of plunger V2 and continued upward movement of plunger V3 will cause slideblock 35 to continue to move upward in respect to Fig. 5 until upward movement of plunger V3 is stopped by stem 150 engaging stop 195. Movement of slideblock 35 above its neutral position will cause pump P1 to discharge liquid through channel 8 to motor 26 which will move table 1 toward the left. The maximum speed of table 1 is determined by the adjustment of stop 195 and the rate at which it is accelerated is determined by the rate at which liquid can flow through choke 163.

Table 1 will move toward the left at the speed determined by the adjustment of stop 195 until dog 191 engages roller 194 and causes lever 192 to gradually lower plunger V3 which will permit the right ends of teeter bar 71 and lever 72 to move downward and permit the pressure in bore 80 to raise plunger V1 to connect cylinder 37 to exhaust and permit servo-motor 40-41 to move slideblock 35 downward in respect to Fig. 5, thereby reducing the displacement of pump P1 and decelerating table 1. Dog 191 will cause lever 192 to lower plunger V3 until piston 141 uncovers a small portion of port 144, at which time slideblock 35 will be approximately in its neutral position and the speed of table 1 will be approximately zero, and then liquid will flow from channel 89 into the upper ends of bores 133 and 142 and cause plungers V2 and V3 to move downward. Plunger V2 willmove into its lower position and will eject liquid from the lower end of bore 133 through channel 123, bore 118and channel 121 into the lower end of bore 142. Plunger V3 in moving downward will eject liquid from the lower end of bore 142 through passage l47, port 144, channel 146, choke 165, port 161, channel 184 and port 180 to exhaust. The rate at which plunger V3 moves downward is proportional to the rate at which it can eject liquid through choke 165. i

Downward movement of plunger V2 and continued downward movement of plunger V3 will cause slideblock 35 to move downward in respect to Fig. 5 until downward movement of plunger V3 is stopped by lever 192 engaging cam 197. Movement of slideblock 35 belowv its neutral position will cause pump P1 to. discharge liquid through channel 7 to motor 26 which will move table 1 toward the right. The maximum speed of table. 1 is determined by the adjustment of cam 197 and the rate it is accelerated is determined by the rate at which liquid can flow through choke 165.

Table 1 will move toward the right until reversal is eifected by dog 190 engaging roller 194, as explained above, and it will continue to reciprocate until the operator stops table 1 such as by opening stop switch SS3. In order that the work may readily be inspected, table 1 may be moved beyond its normal point of reversal at the end of a return stroke by depressing switch SS7 to energize magnet C3 which will close switches C3 (33 and C3 and open switch C3 Opening switch C3 deenergizes magnet C to permit switches C5 and C5 to open and deenergize solenoid 177 which will permit valve 8 to return to its normal position and cause plunger V3 to center itself as previously explained. 1

Closing switches C3 and C3 energizes solenoid 109 whichwill move valve V5 downward to permit pressure toextend into the lower end of bore 133 to hold valve V2 in its upper position. Then table 1 will move toward the left at slow speed until stopped by opening switch SS3.

Modest Jew .side of said circuit and thereby Thereafter, operation may be resumed by depressing switch SS6 which will start table 1 moving toward the right as previously explained.

The hydraulic drive herein set forth is susceptible of various modifications and adaptations without departing from the scope of the invention which is hereby claimed as follows:

1. A hydraulic system comprising a hydraulic motor for driving a load in opposite directions alternatiely, a pump for supplying liquid to said motor to energize the same, fluid channels connecting said pump to said motor and forming therewith a closed hydraulic circuit having interchangeable pressure and return sides, said pump having a displacement varying member normally occupying a neutral position in which pump displacement is zero and shiftable in opposite directions to cause said pump to discharge liquid into one or the other side of said circuit and thereby enable said motor to drive said load in one direction or the other, a relief valve, means for providing communication between the return side of said circuit and said relief valve including a locking valve normally occupying an open position and adapted to close and block said communication in response to movement of said member, and means responsive to movement of said member ceasing for opening said locking valve to re-establish said communication.

2. A hydraulic system comprising a hydraulic motor for driving a load in opposite directions alternately, a pump for supplying liquid to said motor to energize the same, fluid channels connecting said pump to said motor and forming therewith a closed hydraulic circuit having interchangeable pressure and return sides, said pump having a displacement varying member normally occupying a neutral position in which pump displacement is zero and shiftable in opposite directions to cause said pump to discharge liquid into one or the other side of said circuit and thereby enable said motor to drive said load in one direction or the other, servo-motor means for shifting said member and including at least one piston and cylinder, means for supplying liquid to said servo-motor means to cause the same to move said member in opposite directions alternatively, a relief valve, means for providing communication between the return side of said circuit and said relief valve including a locking valve normally occupying an open position and adapted to close and block said communication in response to movement of said piston, and means responsive to movement of said piston ceasing for opening said locking valve to re-establish said communication.

3. A hydraulic system comprising a hydraulic motor for driving a load in opposite directions alternately, a pump for supplying liquid to said motor to energize the same, fluid channels connecting said pump to said motor and forming therewith a closed hydraulic circuit having interchangeable pressure and return sides, said pump having a displacement varying member normally occupying a neutral position in which pump displacement is zero and shiftable in opposite directions to cause said pump to discharge liquid into'one or the other side of said circuit and thereby enable said motor to drive said load in one direction or the other, servo-motor means for shifting said member and including at least one piston and cylinder, means for supplying liquid to said servo-motor means to cause the same to move said member in opposite directions alternatively, a relief valve, means for providing communication between the return side of said circuit and said relief valve including a locking valve normally occupying an open position and adapted to close and block said communication in response to flowof liquid into or out of said cylinder, and means responsive to liquid ceasing to flow into or out of said cylinder for opening said locking valve to re-establish said communication.

4. A hydraulic system comprising a hydraulic motor for driving a load in opposite directions alternately, a pump for supplying liquid to said motor to energize the same, fluid channels connecting said pump to said motor and forming therewith a closed hydraulic circuit having interchangeable pressure and return sides, said pump having a displacement varying member normally occupying a neutral position in which pump displacement is zero and shiftable in opposite directions to cause said pump to discharge liquid into one or the other enable said motor to drive said load in one direction or the other, means-for i 19: creating back presure' in --the -=return side of said circuit including an auxiliary pump-and-airelief valveior:hmit- -ing theqpressure ereated by said auxiliary pump, means :for providing a communication between the return-side of said tcircuit andsaid -auxiliary-pump--and saidrelief valve including a locking valve normally occupying-an :open position and adapted; to c1ose;.and= block {said com -municationin response -to -movement of --said member, and means responsiveto; movement of said {:member ceasingfor opening said locking valve to 're-establishysaid t communi'cation.

5; A hydraulic system comprisinga hydrauliemotor fordriving a1oad-inopposi'te directions alternately, a pump for-supplying; liquid tosaid-;motor-;to;-energize then-same;fluid channels connecting said ;pump;: to said motor and-forming' therewith a closed-hydraulic circuit having-interchangeable pressure ---and return sides, said pump havinga displacement varying member normally :.occupying a-neutra-l position inr'whichypump displace- =:ment .is-ze'ro andsshiftable in-opposite directions to'cause said pumpl to discharge-"liquidinto-"one' -or' the -other side ofsaid circuit' and 1 thereby enable saidmotor. to :drive 's'aid load in--onei'direction--or the other;-servomotor means -for- "shifting;-,-isaid member; and including at least one piston andcylinders-means-for;:supplying liquid to-"said. ser-vo-motor means- 'to cause the. same to :move -said -memberin: opposite directions alternatively, "means for creating back pressure in-the return; side of isaid 2 circuit includingan=-auxiliary "pumpand a relief 'walv'e for limiting thepressure created by ,saidauxiliary :pump, -mean's-for providing communicationbetween' the "return? side of 'saidcircuie and-said auxiliary" pump and wsaid relief valve including -a locking valv'e normally occupying =an open position and adapted-ito close and block said communication in response: to= flow of 1 liquid :into -orout-: ofsaid cylinder; and -means responsive to:;liquid tceasing to :flow ==into f or out ofsaid vc'yljinder for; opening said-docking valve tore-establish "said communication. 374 61 A hy-draulie' system comprising a --hydraulic motor for driving {a loadin opposite directions -alternately, .a .tpump for supplying :li'quid to said motor to energize the same' "flllid channels connecting said pump to js'aid =motor -andforming-therewith a closed hydraulic circuit hayinginterchangeable 'pressure and return ysides, said v ;pump l1a'v-ing--a displacement varyingirmembernormally 1occupying=-aneutral positionin whieh pump idisplace- :rnentdszero and shiftable in-oppositel-=directions=to cause said pump to discharge liquid into one or theotherjlside of said circuit and'iahe'rebyenablefisaid rmotor to, drive .isaid load in one --direction-oru-the' other; a large servotrmotomfor m'oving said member-in one' direction; a small iservo' moto" lfor m'oving -said *member' inigthe opposite id-irection arid=including -a piston-and acyli'nder, avalve =..body elosing-the outer-'end-of? said eylinder -and having \iai bore zformed thereimwitn four ports formed in th e wall thereof; fluidgchannel meansforsconnectiniz the firsb'of ;said ports'to alsource of: pressur'e liquicl. fluid channel cmeans'efore connecting the' secondz -ofi said ports; to-the sneturnczside i of said =circuit, .a-:fluid -channel-connect-ing- 'sthedhird of said ports to 'ssaidi cyllinder, a'springccntered clocking ,valveiarranged inisaidi bore toeontrol said ports mind having; itsuinner; endmsubjectedi to :thepressure" in t 'aide; cylinder zsaid :valve:inormallya occupying ta :position mswhicheaitlssecond port isaopen; toa's'aid first port' and :abeingashiftable ini-tone, direction: ortr theaoth r; {unbl ck r0116; orstheother" of: said: first. and second ports, =a source bfipressure liquid zmeansforzsupplying:liquidjrom:said :.sour.cetonthe riourthwofisaid portsaand to theyouter end of- :said lo k g valve:- to ntberebyiimaintain --in :said -cylninder'l-thersflme pressurezzthahpnevails atisaid source rand mqans including zaflpilotnvalve for connectingisaid large servo-motor to said sourceicand LtQYQeXhauSt'i selectively. 7.- Aahydrauliesysternzcomprising avhydrauliemotor eforkdriving aa load in opposite directionsalternately, a ipumpsfor; supplying: l-iquidifto; -I sai d :moton to ener gize c-the same',ufiuidi:channelsa:connecting=said-pump to said nmotorrand aforminghtherewith a -closed hydraulic circuit 1 having:Jinterehangeable pressure: andreturn sides; said i pump havingsa: displacement-varying member-normally occupying a =neutral position 'in w h ichpump displace- "ment is; zero and shiftable irr-ppposite directions to cause said pump I to discharge liquid into 'o neor the-other side '"of s'aid circuit --and-thereby-enable said -,rnotor. to drive said el'oad "in onedirection" orthe" other, an auxiliary 50 motor means to cause the same to move said member pump for maintaining pressure in both sides of said circuit Land only-when saidmernberis in its neutral position, a relief -valvekfor li :t P es u e; created abyx a siia r l a y pump, and means fqr gonnectin a auxjliary pum and rsaid relief o ha is 0t; a l r ui ,mslu n ablocking valve' responsive-to movement; of said 'r nember away from its neutral position, for blocking communication between;said;relief valve and the side 01f said circuit which is the'pressureside? 8, A hydraulic system-comprising a hydraulic mqtor for-"driving a load;in,oppo'site directions" alternately, a pump for supplying liquid to said motor'to energize the I same fiuid channels connecting said pump to. said motor and-forming therewith a closedthydraulic circuit having interchangeable pressure and return: sides ,'gsaid p ump having a displacement varying member normally cgupying a neutral'po sition in which pump displacement is Zero and shiftable in-oppositedirections to cause said pump to discharge liquid into one or ,therother side "of said circuit and thereby enable said motor 'to "drive said ,load in one: directionyor the other a largeservo n otor for moving;.said member in one direction, a small servomotor for moving said member in the opposite direction andincluding' a piston and a cylinder; means for; efiecting operation of saids'ervomotors to cause the same tqmove i'saidf member inopposite directions selectively, a valve body-closing the outer end of said cylinder and haying a'bo're formed therein with a center portjand two end po ts ormed n t '1: h e n aux ia ysp p. maintaining pressure in both sides ofsaid circuitonly when said member is in its neutral position, a relief valve for limiting the pressure createdv by said auxiliary pump, means; for connecting 's aid center port to said auxiliary ,pump;- cl 1an ne1s; connecting ;s aid two end-ports to the twofsidfes ot said circuit respectively, andablocking yalve fitted ins saidbore and movable with said piston-into a position'to block. communication between said center port and one ofisaid end ports 'inresponse to movement of said piston in one direction and movable into apposition ,tqblock cqmmunication between said centerpo'rt andthe jother' of said end portsin responsertomovement of said piston in the opposite direction.

'9.Ahydraulicsystemcomprising a hydrauli c motor ;fo r drivingaf load in opposite-directions alternately, a pump f( r. su p plying liquid to saidrnotor. to, energizethe .$.@I! ,;;fiuid 5:hanne1s connecting said ,pump. to s'aidmotor ndtorming therewith a closed hydraulic.circuithaving n rchangeable pressure and return sides, said pump having, aj displacement varying member normally: occupying aneutral position'inwhich pump displacement. is zero and fshiftable in opposite directions to cause said -pump to, ,discharge liquid into, one or the other side, of said, circuitIand thejrebyenable,saidmnotor to ,drive said 198d in onedirection or the other, an auxiliary pump. for maintaining pressure in both sides of said circuit only .whendsaid. member, is in its, neutralflposition', a relief valve-tor limiting .the :pressure. createdbyjsaid auxiliary purnp means '.for connecting saidauxiliary pump v and ;said,r elie'f,;valve toboth-sides of said circuit including a blocking valve. responsive to ;movement ofi -said rnember .is'pon e t rem t qfl a d mem e a d m ns mp9ssive to amovernent; of; said. member ;c eas 1ng foropenmg said locking. valve to re-establish said communication.

it, 10. Ahydraulic systernvvcomprisinga I hydraulic l motor for driving a loa'd in ,oppo'site; directions alternately, a nump r p ly ns l q i tos id mom t energizer-the sa e,fluidchannels connecting said.pump dmotor -.-fo mi gtt ew t lose y rau wither interchangeable pressure and ,return sides, :isaid, 'p'fimp ,haying a' .,d 'splacement. yarying member f'norrnally pccupying a neutral position inffwhichpump displacement is zteror and shittable inyopposite directions to cause, said pump, to.dischargeliquid .into-, one, or theother. side of said circuit and thereby tenable; said motor 1 to drive; said load .in. onc direction or.,the other,'ts ervo-mo'tor means for shiftin'gsaid memberand includingat least one /piston and'cylindei', means for'supplyin'g liquid to said servo- 18. A combination as set forth in claim 17 including a high speed choke connected between said control valve and each of said ports, a low speed choke connected in parallel with each of said high speed chokes, and an acceleration selector valve connected between said chokes and said control valve for blocking communication between said control valve and either said low speed chokes or said high speed chokes.

19. In a hydraulic system having a hydraulic motor for driving a load in opposite directions alternately, a pump for supplying liquid to said motor to energize the same, fluid channels connecting said pump to said motor and forming therewith a closed hydraulic circuit having interchangeable pressure and return sides, said pump having a displacement varying member normally occupying a neutral position in which pump displacement is zero and shiftable in opposite directions to cause said pump to discharge liquid into one or the other side of said circuit and thereby enable said motor to drive said load in one direction or the other, and servo-motor means for shifting said member in one direction or the other, the combination of means for supplying pressure liquid to said servo-motor means to energize the same and including a pilot valve for controlling the fiow of liquid to and from said servo-motor means, said pilot valve normally occupying a neutral position in which it cuts oil flow of liquid to or from said servo-motor means and being shiftable in one direction or the other from said neutral position to direct liquid to or from said servomotor means to thereby cause said servo-motor means to move said member in one direction or the other, a slow speed plunger and a reversing plunger each normally occupying a neutral position and being shiftable in one direction or the other to effect movement of said pilot valve in one direction or the other, a follow-up mechanism responsive to movement of one or both of said plungers for effecting movement of said pilot valve away from its neutral position and responsive to movement of said member for effecting movement of said pilot valve toward its neutral position, means for initially shifting said slow speed plunger to the limit of its movement in one direction or the other, and means for thereafter shifting said reversing plunger to the limit of its movement in a direction corresponding to the direction in which said slow speed plunger was shifted.

20. A combination as set forth in claim 19 and including means responsive to said load approaching the limit of its movement in one direction or the other for shifting said reversing plunger to a point beyond its neutral position from the position to which it was previously moved, means responsive to said reversing plunger reaching said point for continuing the movement of said reversing plunger to the limit of its movement, and means'responsive to said reversing plunger reaching said point for shifting said slow speed plunger to the limit of its movement in a direction corresponding to the direction in which said reversing plunger was just moved.

21. In a hydraulic system having a hydraulic motor for driving a load in opposite directions alternately, a pump for supplying liquid to said motor to energize the same, fluid channels connecting said pump to said motor and forming therewith a closed hydraulic circuit having interchangeable pressure and return sides, said pump having a displacement varying member normally occupy- A 24 ing a neutral position in which pump displacement is zero and shiftable in opposite directions to cause said pump to discharge liquid into one or the other side of said circuit and thereby enable said motor to drive said load in one direction or the other, and servo-motor means for shifting said member in one direction or the other, the combination of means for supplying pressure liquid to said servo-motor means to energize the same and including a pilot valve forcontrolling the flow of liquid to'and from said servo-motor means, said pilot valve normally occupying a neutral position in which it cuts off flow of liquid to or from said servo-motor means and being shiftable in one direction or the other from said neutral position to direct liquid to or from said servo-motor means to thereby cause said servo-motor means to move said member in one direction or the other, a slow speed plunger and a reversing plunger each normallyoccupying a neutral position and being shiftable in one direction or the other to effect movement of said pilot valve in one direction or the other, a follow-up mechanism responsive to movement of one or both of said plungers for effecting movement of said pilot valve away from its neutral position and responsive to movement of said member for effecting movement of said pilot valve toward its neutral position, means including a low speed valve for initially shifting said low speed plunger to the limit of its movement in one direction or the other and for initially shifting said reversing plunger away from its neutral position in a direction corresponding to the direction in which said low speed plunger was moved, means including a high speed valve for shifting said reversing plunger to the limit of its movement in response to it being moved away from its neutral position, means responsive to said load approaching the limit of its movement in-one direction or the other for shifting said reversing plunger to a point beyond its neutral position from the position to which it was previously moved, and means responsive to said reversing plunger reaching said point for shifting said slow speed plunger to the limit of its movement in a direction corresponding to the direction in which said reversing plunger was just moved.

22. A combination as set forth in claim 21 in which said means for initially shifting said low speed plunger includes a starting valve to cooperate with said low speed valve and eifect initial movement of said low' speed plunger, a first solenoid for shifting said starting valve, a second solenoid for shifting said low speed valve, a third solenoid for shifting said high' speed valve, and an electric circuit including a starting switch, means responsive to closing said starting switch for energizing said first and said second solenoids, means responsive to opening said starting switch for deenergizing said first solenoid and energizing said third solenoid, and means responsive to'said starting switch being closed after said third solenoid is energized for deenergizing said third solenoid.

References Cited in the file ofthis patent UNITED STATES PATENTS 2,227,814 Tyler Jan. 7, 1941 2,240,898 Wiedmann May 6, 1941 2,465,212 Douglas Mar. 22, 1949 2,497,608 Herrstrum et a1. Feb.. 14, 1950 

